<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Home</title>
</head>
<body>
    <h1>Hello world</h1>
    <br>
    <h3 id="a" style="text-align: center;color: blue;">Click Me!!</h3>
    <button onclick="alertme()">Click Here!!</button>
     <script>
        function alertme(){
            document.getElementById("a").innerHTML = "What's Up!!!";
        }
    </script>
</body>
</html>
